1. Field of the Invention
The present invention relates to reactors useful in chemical or physical vapor transport crystal growth.
2. Description of the Prior Art
In order to study the characteristics and properties of highly ordered films or crystals of organic or inorganic materials, it is desirable to produce crystals or films which excel in purity, homogeneity and size. One method of increasing the quality of these films or crystals ("crystals" hereafter will include films) is physical vapor transport crystal growth wherein a solid source material is heated above its vaporization temperature and the vapor allowed to crystallize on a platen cooled below the crystallization temperature of the material. Another method is chemical vapor transport crystal growth wherein the source material reacts with another material while in the vapor state.
The source material is contained within the closed end of a glass tube into which is inserted a deposition surface, which may be a platen of metal or a semiconductor material, upon which the source material vapors may crystallize. The source material is heated above its vaporization temperature by heating elements surrounding the glass tube and the platen within the tube is cooled below the crystallization temperature of the source material by connecting the platen to a heat sink.
One material whose crystals are commonly produced by this method is GeSe which must be heated to approximately 520 degrees C. for vaporization while the platen must be cooled to approximately 420 degrees C. to promote crystallization. To control the crystals produced, the glass tube is usually evacuated of air and filled with a buffer or transport gas which is either inert with respect to the source material at its vaporization temperature or which reacts in a controlled manner with the source material. A transport gas useful in the production of GeSe crystals is GeI.sub.4, which may be present in the tube at a partial vacuum throughout or at pressures above atmospheric. To contain the vacuum or pressure within the glass tube, the glass tube is sealed in present reactors by fusing the tube directly to the platen or to a heat conductive bar extending from the platen. This sealing method causes problems and has serious disadvantages because the tube must be broken to obtain the crystals and the entire glass-tube/platen assembly must be replaced. Breakage of the glass tube may also fracture or contaminate the crystals and render them useless for experimental purposes.
Recently it has been found that superior crystal growth can be achieved in microgravity environments such as those found aboard orbiting vehicles. The cost of experiments under these conditions is extremely high and loss of experimental samples is disastrous because the opportunities for future experiments are infrequent.